I don't think you will be able to do a "good" Dark Urge. From the RockPaperShotgun preview :
Some of the Urge’s setpieces have a dissociative quality. At one point, while passing through a druid’s grove, Ding encouraged me to go and say hello to a squirrel. Before I knew it, the camera had snapped to a nearby tree, just in time to see the squirrel’s body splatted against the bark. It’s a scene that demonstrates Larian’s growing confidence with cinematic staging - distancing you uncomfortably from your own actions by keeping them out of frame.
Yet the squirrel was just the start of it. Back at camp, I tucked myself into bed, only to discover a brutalised corpse of my own making during the night. There followed a sequence in which I was given the option to marvel at my handiwork, wash my hands of blood, and hide the body in the bushes. Most intriguingly of all, the whole sequence played out beyond the view of my co-op partner - leaving it up to me to confess the crime, or not. It strikes me as a classic tabletop dynamic - with one player given the choice to hide their cards, and delight in the transgressive glee of keeping a secret from the table.
This isnt indicative of not being able to do a good dark urge at all, quite the opposite imo.
The game starts you off with the dead squirrel, to introduce you to the outcome of giving in to the dark urges, as right after you get an important decision wih Gale. Same goes for the episode in the camp, it is directly followed by a choice in dialogue, of either swearing to resist or give in to these temptations from that point forward, acting as a introduction to the character and opportunity to decide which direction to go with it.
As far as Ive seen and heard, (i.e fextralife) after that you will have the choice to resist. There might be some more of these moments of waking up after something terrible has happened, but my guess is that that would be unique episodes related to the origins quest, rather than interfering with or "ruining" other quests. I highly doubt that dark urge simply forces you into a single evil outcome against your will for quests and companion relationships, as what seems like their biggest selling point is to give the player as many directions to go in with the story as possible.
Might be wrong, but imo that would be extremely unlikely and unexpected given larians design philosophy from what we've seen and heard so far.
